Method for Defining Patterns for Conductive Paths in a Dielectric Layer

ABSTRACT

An example embodiment may include a method for defining patterns for conductive paths in a dielectric layer. The method may include (a) forming a mask layer on the dielectric layer, (b) forming on the mask layer a set of longitudinally and parallel extending mask features, each mask feature including a mandrel having a pair of side wall spacers, the mask features being spaced apart such that gaps are formed between the mask features, (c) depositing an organic spin-on layer covering the set of mask features and filling the gaps, (d) etching a first trench in the organic spin-on layer, the first trench extending across at least a subset of the gaps and exposing the mask layer, and (e) depositing in a spin-on process a planarization layer covering the organic spin-on layer and filling the first trench.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a non-provisional patent application claimingpriority to European Patent Application No. EP 17158033.5, filed Feb.27, 2017, the contents of which are hereby incorporated by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates to a method for defining patterns forconductive paths in a dielectric layer.

BACKGROUND

Modern circuit fabrication typically includes processes of formingelectrical interconnection structures for interconnecting semiconductordevices in a functioning circuit. An interconnection structure mayinclude one or more metallization levels or tiers, which are formedabove the substrate and the semiconductor devices. A metallization levelincludes conductive paths or lines arranged in a dielectric materiallayer. The dielectric material layer of a metallization level mayisolate the conductive paths of the metallization level from a higherand/or a lower metallization level. Conductive paths of differentmetallization levels may be interconnected by conductive vias extendingthrough the dielectric layers.

A metallization level may be formed by forming patterns includingtrenches and holes in a dielectric layer, and filling the trenches andholes with a conductive material. Such a process may be referred to as adual damascene process. The process may be repeated to form a stack ofmetallization levels on top of each other.

Patterns may be formed in a mask layer arranged above the dielectriclayer using lithographic techniques and etching. Multiple patterningtechniques like (litho-etch)x, or pitch splitting techniques such asself-aligned double patterning (SADP) or quadruple patterning (SAQP),may be used to enable patterns with sub-lithographic criticaldimensions. Multiple patterning may be combined with block techniques toenable forming of interrupted or discontinuous lines.

SUMMARY

The present disclosure may provide an improved method for definingpatterns for conductive paths in a dielectric layer. According to anaspect of the disclosure there is provided a method for definingpatterns for conductive paths in a dielectric layer, the methodcomprising (a) forming a mask layer on the dielectric layer, (b) formingon the mask layer a set of longitudinally and parallel extending maskfeatures, each mask feature including a mandrel having a pair of sidewall spacers, the mask features being spaced apart such that gaps areformed between the mask features, (c) depositing an organic spin-onlayer covering the set of mask features and filling the gaps, (d)etching a first trench in the organic spin-on layer, the first trenchextending across at least a subset of the gaps and exposing the masklayer, (e) depositing in a spin-on process a planarization layercovering the organic spin-on layer and filling the first trench, (f)reducing a thickness of the planarization layer and the organic spin-onlayer by etching until upper surfaces of the mask features are exposed,thereby forming, of remaining material of the planarization layer, adiscrete first block mask in each gap of the subset of gaps, (g)removing remaining organic spin-on material between the mask features,selectively to each first block mask, thereby exposing the mask layer inthe gaps between the mask features, and (h) etching the mask layer inthe gaps, thereby forming a first set of trenches in the mask layer, atleast one of the trenches being interrupted in a longitudinal direction.

The method enables definition, in a mask layer, of patterns forconductive paths or conductive lines in a dielectric layer of ametallization level. The patterns may be formed as trenches in the masklayer and subsequently transferred into the dielectric layer.

The position and dimension of the trenches may be established by the setof mask features. Mask features including mandrels having pairs of sidewall spacers may be formed by techniques (such as multi patterningtechniques) enabling sub-lithographic feature sizes.

Each first block mask enables forming of a discontinuous or interruptedtrench, each discontinuous trench including a first and a second trenchportion on opposite sides of a first block mask. Conductive lines with atip-to-tip configuration may thereby be formed in the dielectric layer.

By forming the first block mask using the first trench in the organicspin-on layer, the first block mask may be formed in a self-alignedmanner with respect to the gaps between the mask features. The presenceof the mandrels will counteract forming of a block mask at anon-intended position between a pair of side-wall spacers of a mandrel.The dimensional and alignment requirements during the forming of thefirst block mask may thereby be relaxed.

The deposition of an organic spin-on layer may provide several benefits.For example, covering the set of mask features and filling the gaps withan organic spin-on layer may enable efficient definition of thepositions of the first block mask. An organic spin-on layer may bedeposited relatively quickly and in a self-planarizing manner. Thisobviates any need for a separate planarization step (e.g. by chemicalmechanical polishing, CMP) prior to forming the first trench. An organicspin-on layer may also provide a comparably strong etch contrast withrespect to materials typically used for mandrels and side wall spacers.This provides selective removal of the organic spin-on layer withrespect to the side wall spacers and the mandrels. An organic spin-onlayer is also possible to etch using non-Chloride based etchingchemistries.

Forming the planarization layer by a non-metal based material (such as asilicon-including spin-on material) hence provides Chloride-basedetching chemistries to be avoided for the purpose of defining thepatterns. This enables a reduced cost process.

The deposition of a planarization layer in a spin-on process may provideseveral benefits. For example, spin-on deposition processes arecomparably time efficient processes compared to other depositionprocesses such as chemical vapor deposition (CVD) and atomic layerdeposition (ALD). Spin-on deposition also enables the trench to befilled comparably quickly with the material of the planarization layer.Moreover, as the planarization layer is deposited in a spin-on process,the planarization layer may be deposited in a self-planarizing manner.Hence, the thickness reduction for exposing mask features may beachieved by etch back, without a preceding CMP step. The deposition of aplanarization layer in a spin-on process hence contributes to an overallefficiency of the process.

Since the material forming the planarization layer is directly depositedin the gaps at the intended positions (as defined by the position of thefirst trench) no separate patterning and etching of the planarizationlayer is required. Consequently, it is not required that the materialforming the planarization layer provides an etch contrast compared tothe material forming the side wall spacers. This provides flexibility inthe selection of materials.

During the etching of the mask layer in the gaps between the maskfeatures, the side wall spacers and each first block mask may act as acombined etch mask.

Generally, the set of mandrels may be formed by a first material, theside wall spacers may be formed by a second material and the mask layermay be formed by a third material, wherein the first, the second and thethird material are different materials. The first material may be etchedselectively from the second material. The third material may be etchedselectively from the first and the second material. The first materialmay be etched selectively from the organic spin-on layer. The firstmaterial may be etched selectively from the planarization layer. Thethird material may be etched selectively from the third material. Theorganic spin-on layer and the planarization layer may be formed ofdifferent materials. The organic spin-on layer may be etched selectivelyfrom the planarization layer. In this context, a material “A” which maybe etched selectively from a material “B” means that material A may beetched at a substantially greater rate than material B, in a given etchprocess. In other words, a feature of material A arranged adjacent to afeature of material B may be removed in an etch process withoutappreciably affecting the feature of material B.

The organic spin-on layer is formed by a spin-on-carbon layer.

The planarization layer may be formed by a silicon-including spin-onmaterial. The planarization layer may be formed by a silicon-includingspin-on material, for instance spin-on SiOx or spin-on SiOC. Themandrels may include amorphous silicon (a-Si), strained a-Si, or siliconnitride. The side wall spacers may include silicon oxide or siliconnitride.

The mask layer may be formed on the dielectric layer. The mask layer maybe formed directly on the dielectric layer or with one or moreintermediate layers between the dielectric layer and the hard masklayer.

The mask layer may be any layer or layer stack having the ability towithstand, and accordingly remain following, the removal of the metaloxide planarization layer. The mask layer may for instance be anon-resist based mask layer. The mask layer may be a “hard” mask layer.The mask layer may include titanium nitride, titanium oxide, hafniumoxide or zirconium oxide.

The mask layer may include a stack of a first material layer and asecond material layer. The second material layer may be a buffer layerfor facilitating forming of the set of mandrels above the first materiallayer. The second material layer may improve the overall etch stoppingstrength of the mask layer during the etch steps preceding the patterntransfer into the mask layer.

The first material layer may include titanium nitride, titanium oxide,hafnium oxide or zirconium oxide and the second material layer mayinclude silicon nitride or silicon oxide. A silicon nitride layer mayfacilitate forming of amorphous silicon mandrels on the mask layer. Asilicon oxide layer may facilitate forming of silicon nitride mandrelson the mask layer.

The mandrels of the set of mask features may interchangeably be referredto as cores or mandrel lines. The mandrels may extend in parallel toeach other. The side wall spacers may be referred to as spacer lines.Each mask feature may accordingly include a mandrel line arranged inbetween a pair of spacer lines.

The set of mask features may be formed using a multiple patterningprocess such as SADP or SAQP.

By a first feature such as a layer, a level or other structure, beingformed “above” a second feature such as a layer, a level or otherstructure, is hereby meant that the first feature is formed above thesecond feature (as seen) in a normal direction to the main surface orin-plane extension of the feature, e.g. layer or level, or equivalentlyin the normal direction to a substrate on which the metallization levelis to be formed.

By a first feature such as a layer, a level or other structure, beingformed “on” a second feature such as a layer, a level or otherstructure, is hereby meant that the first feature is formed directly onthe second feature, i.e. in abutment with the second feature, or withone or more layers intermediate the first and the second feature, i.e.not in direct contact with the second feature.

By “metallization level” is hereby meant a structure includingconductive paths arranged in a dielectric material layer. The method maybe repeatedly performed for definition, in a mask layer, of patterns forconductive paths or conductive lines in a dielectric layer of two ormore metallization levels to form a stack of metallization levels.

By a “trench” in a layer (e.g. in the mask layer or in the dielectriclayer) is hereby meant a recess in the layer. A trench may, at leastalong a portion thereof, extend in a straight line and presents auniform width.

According to one embodiment the method further comprises, subsequent toreducing the thickness of the planarization layer and the organicspin-on layer: (a) depositing an organic spin-on layer covering the setof mask features and each first block mask, (b) etching a second trenchin the organic spin-on layer, the second trench extending across andexposing at least a subset of the mandrels, and further etching eachmandrel of the at least a subset of mandrels in the second trench,selective to the organic spin-on layer, to expose the mask layer, (c)depositing in a spin-on process a planarization layer covering theorganic spin-on layer and filling the second trench, (d) reducing athickness of the planarization layer and the organic spin-on layer byetching until upper surfaces of the mask features are exposed, therebyforming, of remaining material of the planarization layer, a discretesecond block mask along each mandrel of the at least a subset ofmandrels, (e) removing the set of mandrels, selectively to each secondblock mask, thereby exposing the mask layer between each pair of sidewall spacers, and (f) etching the mask layer between each pair of sidewall spacers, wherein each second block mask act as an etch mask,thereby forming a second set of trenches in the mask layer, at least oneof the trenches being interrupted in a longitudinal direction.

The use of an organic spin-on layer and planarization layer in thepresent embodiment provides benefits corresponding to those discussed inconnection with the main method aspect above. The various types ofmaterials for the organic spin-on layer and the planarization layerdiscussed in connection with the main method aspect above appliescorrespondingly to this embodiment.

The present embodiment enables a doubled line density in that the firstset of trenches may be formed by etching in the gaps between the maskfeatures and in that the second set of trenches may be formed betweenthe pairs of side wall spacers.

Each second block mask enables a trench of the second set of trenches tobe formed as a discontinuous or interrupted trench, each discontinuoustrench including a first and a second trench portion on opposite sidesof a second block mask. Conductive lines with a tip-to-tip configurationmay thereby be formed in the dielectric layer, also at positions definedby the second set of trenches.

By forming the second block mask using the second trench, the secondblock mask may be formed in a self-aligned manner with respect to a pairof side wall spacers. By etching each mandrel exposed in the secondtrench, selective to the organic spin-on layer, between a pair of sidewall spacers, the presence of remaining material of the organic spin-onlayer between mask features will counteract forming of a second blockmask at a non-intended position between mask features. The dimensionaland alignment requirements during the forming of the second block maskmay thereby be relaxed.

The first and second set of trenches in the mask layer may be etchedsimultaneously, i.e. in a same etching process. In other words, etchingthe mask layer may include etching the mask layer in the gaps andbetween each pair of side wall spacers, wherein the side wall spacers,each first block mask and each second block mask act as a combined etchmask, the etching thereby forming a first set of trenches and a secondset of trenches in the mask layer, at least one of the first set oftrenches and at least one of the second trenches being interrupted in alongitudinal direction. The total number of etching steps for forming apattern in the mask layer may thereby be limited.

The act of removing remaining organic spin-on material between the maskfeatures may be performed subsequent to forming the one or more secondblock mask. Thereby, material portions of the first deposited (first)organic spin-on layer remaining in the gaps between the mask featuresmay be re-used during the forming of the second block mask(s). Thenumber of etch steps to which the side wall spacers and the mask layerare exposed may thereby be limited.

According to one embodiment the method further comprises: transferringthe trenches in the mask layer (i.e. the first set of trenches and, asthe case may be, also the second set of trenches) into the dielectriclayer. The remaining portions of the mask layer (possibly together withany side wall spacers and first and second block masks remaining on themask layer) may act as an etch mask, counteracting etching of regions ofthe dielectric layer covered by the remaining portions of the masklayer.

The method may further comprise filling the trenches in the dielectriclayer with a conductive material.

The trenches may be at least partially filled with a conductivematerial. The conductive material may be a single metal or a mixture oralloy of a metal and another material. A complete filling of thetrenches may allow the entire cross-sectional area, allowed by thetrenches in the dielectric layer, to be filled by the conductivematerial to obtain a low-resistance interconnect structure.

The act of filing with a conductive material may comprise forming theconductive material also above the dielectric layer and removing theconductive material in locations outside of the trenches of thedielectric layer and the deepened first and second holes. The removingof excess conductive material may divide the deposited conductor intoseparate paths extending within the trenches of the dielectric layer.

BRIEF DESCRIPTION OF THE FIGURES

The above, as well as additional, features will be better understoodthrough the following illustrative and non-limiting detailed descriptionof example embodiments, with reference to the appended drawings.

FIGS. 1a-1m schematically illustrate a method for defining patterns forconductive paths in a dielectric layer, according to an exampleembodiment.

All the figures are schematic, not necessarily to scale, and generallyonly show parts which are necessary to elucidate example embodiments,wherein other parts may be omitted or merely suggested.

DETAILED DESCRIPTION

Example embodiments will now be described more fully hereinafter withreference to the accompanying drawings. That which is encompassed by theclaims may, however, be embodied in many different forms and should notbe construed as limited to the embodiments set forth herein; rather,these embodiments are provided by way of example. Furthermore, likenumbers refer to the same or similar elements or components throughout.

A method for defining patterns for conductive paths in a dielectriclayer will now be described with reference to FIGS. 1a -m.

FIG. 1a shows, in perspective, a section of a semiconductor structure orintermediate device 100. The structure 100 may extend laterally orhorizontally beyond the illustrated section. The illustrated planes ofsection extending through the structure 100 are common to all thefigures.

It is noted that the relative dimensions of the shown elements, inparticular the relative thickness of the layers, is merely schematic andmay differ from practice for the purpose of illustrational clarity.

The structure 100 includes in a bottom-up direction a semiconductorsubstrate 102. An active device layer 103 including semiconductordevices such as transistors are fabricated on a main surface of thesubstrate 102. The active device layer 103 may also be referred to as afront-end-of-line portion (FEOL-portion 103). In FIG. 1a , a firstmetallization level 104, including conductive lines arranged in adielectric layer, is formed above the FEOL-portion 103. A base layer 105is formed on the first metallization level 104. The base layer 105 mayinclude a SiCN layer.

The structure 100 includes a dielectric layer 106. The dielectric layer106 forms a dielectric layer of the metallization level which is to beformed. The dielectric layer 106 may include a silicon oxide layer, forinstance SiO₂, or another low-K dielectric material. Although not shownin FIG. 1a , the dielectric layer 106 may include a stack of layers ofdifferent dielectric materials, such as an interface layer and/or anoxide capping layer.

A mask layer 108 is formed on the dielectric layer 106. The mask layer108 covers an upper surface of the dielectric layer 106. The mask layer108 may form a hard mask layer. The mask layer 108 may include a singlelayer of for instance titanium nitride, titanium oxide, hafnium oxide orzirconium oxide. The mask layer 108 may alternatively, as shown in FIG.1a , include a stack of a first material layer 109 and a second materiallayer 110 arranged on the first material layer 108. The mask layer 108may include a stack of a layer of titanium nitride, titanium oxide,hafnium oxide or zirconium oxide and a layer of silicon nitride orsilicon oxide, for instance SiO₂. The mask layer 108, or the sub-layers109, 110 thereof, may be formed by atomic layer deposition (ALD).

A set of mask features are formed on the mask layer 108, each maskfeature including a mandrel 112 and a pair of side wall spacers 114 a,114 b. FIG. 1a shows three mask features, however this is merely anillustrational example and typically a greater number of mandrels may beformed above the mask layer 108. The mandrels 112 form elongatedstructures, or lines, extending in parallel to each other.

Each mandrel 112 is provided with a respective pair of side wall spacers114 a, 114 b. Each pair of side wall spacers 114 a, 114 b is formed by afirst side wall spacer 114 a, formed on a first side wall surface of amandrel 112, and a second side wall spacer 114 b, formed on a secondside wall surface of the mandrel 112. The first and second side wallsurfaces are opposite side wall surfaces of the mandrel 112.

The mask features are spaced apart such that longitudinally extendinggaps 113 or spaces are formed between adjacent mask features. Each gap113 is formed between a first side wall spacer 114 a on a first mandrel112 and a second side wall spacer 114 b on a second mandrel 112, next oradjacent to the first mandrel.

Each gap 113 defines the position of a trench of a first set of trencheswhich are to be formed in the mask layer 108. Each mandrel 112 definesthe position of a second set of trenches which are to be formed in themask layer 108.

The mandrels 112 with the side wall spacers 114 a, 114 b may be formedusing multiple patterning techniques:

According to an SADP-process, a mandrel layer may be formed on the masklayer 108. The mandrel layer may be formed by an a-Si layer, such as astrained a-Si layer. Alternatively, the mandrel layer may be formed by aSiN layer. The mandrel layer may be deposited by ALD, or by physicalvapor deposition (PVD) or some other conventional thermal depositionprocess.

A resist-based mask layer (not shown in FIG. 1a ) may be deposited onthe mandrel layer. The resist-based mask layer may be deposited in aspin-coating process. A pattern for defining the mandrels 112 may beformed in the resist-based mask layer using single- or multiple exposurelithography. The pattern of the resist-based mask layer may betransferred into the mandrel layer by etching, thereby forming themandrels 112. The mandrels 112 may thereafter be covered by a conformalspacer material layer. The spacer material layer may for instance be ofsilicon oxide, such as SiO₂, or of SiN. The spacer material layer may bedeposited in an ALD process. Physically separated side wall spacers 114a, 114 b may be formed by anisotropically etching the spacer materiallayer such that the spacer material layer remains only on the sidewallsof the mandrels 112.

According to a SAQP-process two mandrel layers may be used, a top and abottom mandrel layer. A first set of mandrels may be formed in the topmandrel layer in similar manner as in the SADP-process. A first set ofside wall spacers may be formed on the first set of mandrels in similarmanner as in the SADP-process. The first set of mandrels may thereafterbe removed selectively from the first set of side wall spacers byetching. The bottom mandrel layer may thereafter be etched using thefirst set of spacers as an etch mask, wherein the pattern defined by thefirst set of spacers may be transferred to the bottom mandrel layer,thereby forming the set of mandrels 112 shown in FIG. 1a . The side wallspacers 114 a, 114 b may thereafter be formed in a corresponding manneras the first set of side wall spacers, following removal of remainingportions of the top mandrel layer.

The first set of mandrels may in principle also be produced by a linedoubling process such as the above-described SAQP-process. Althoughthere is in principle no limit in the number of line doubling processesthat can be used, each doubling process however becomes more technicallychallenging. Hence, in practice a limit, dependent inter alia onaccuracy of equipment and control of process conditions does exist.

In FIG. 1b , an organic spin-on layer 116 has been formed to cover theset of mandrels 112 and the side wall spacers 114 a, 114 b. The organicspin-on 116 fills the gaps 113 between the mask features. The organicspin-on layer 116 may be formed by a spin-on-carbon (SOC) layer or someother organic spin-on layer which is free from silicon.

A patterned resist-based mask layer 120 is formed on the organic spin-onlayer 116. The mask layer 120 is patterned to include at least onetrench, extending in a direction transverse to the longitudinaldirection of the mask features.

As shown in FIG. 1b , an intermediate layer 118 may be arranged betweenthe organic spin-on layer 116 and the mask layer 120. The intermediatelayer 118 may include a spin-on-glass layer (SOG), a thin layer of SiO₂,a-Si, SiON or SiOC. An intermediate layer 118 may be used for improvingthe fidelity of a transfer of the pattern of the patterned resist-basedmask layer 120 into the organic spin-on layer 116.

In FIG. 1c the pattern defined by the patterned resist-based mask layer120 has been transferred into the organic spin-on layer 116 by etchingwhile using the mask layer 120 as an etch mask. The layer 116 may beetched using a fluorine-based etch chemistry. The mask layer 120 maythereafter be stripped, optionally along with the intermediate layer118, if present. At least one first trench 116′ has accordingly beenformed in the organic spin-on layer 116. The first trench 116′ extendsacross the gaps 113 and exposes an upper surface of the mask layer 108within the gaps 113. In FIG. 1c , a portion of the layer 116 has beencut-out to allow viewing inside the trench 116′.

FIGS. 1b and 1c illustrate forming of two trenches 116′. However thismerely represents an example and fewer or more trenches 116′ may beformed in a corresponding manner, to form a desired number of trenchinterruptions. Also, FIGS. 1b and 1c illustrate forming of a trench 116′extending across at least three mandrels 112. However, this merelyrepresents an example and the trench 116′ may be formed to extend acrossonly one, only two or more than three mandrels 112.

In FIG. 1d the structure 100 has been covered with a planarization layer122. The planarization layer 122 planarizes the structure 100. Theplanarization layer 122 covers the organic spin-on layer 116 and fillsthe trenches 116′. The planarization layer 122 further fills theportions of the gaps 113 extending inside the trenches 116′.

The planarization layer 122 is deposited in a spin-on process. Theplanarization layer 122 may be formed by a silicon-including spin-onmaterial, for instance a silicon oxide-including spin-on material, e.g.SiOx or SiOC. The material which is to form the final planarizationlayer 122 may be dissolved in a solvent. The solvent may be evaporatedduring and/or subsequent to forming a thin film by spinning thestructure 100, wherein the previously dissolved material may remain onthe structure 100 to form the planarization layer 122.

In FIG. 1e the thickness of the planarization layer 122 has been reducedto expose an upper surface of the mask features including the mandrels112. As shown, portions of the side wall spacers 114 a, 114 b previouslycovered by the organic spin-on layer 116 may also be exposed.

As shown, remaining material of the planarization layer 122 formdiscrete first block masks 122′ in each gap of the gaps 113 which wereexposed during the forming of the trenches 116′. Portions of the organicspin-on layer 116 remaining in the gap are arranged on opposite sides ofeach first block mask 122′.

Owing to the self-planarizing property of the planarization layer 124,the thickness reduction may be achieved by an etch-back process, withoutrequiring a preceding planarization step (e.g. by CMP). The etch back ofthe planarization layer 122 may include a dry etch process. Afluorine-based etching chemistry may be used. The etch-back may beperformed until the upper surface of the mandrels 112 is exposed.

As illustrated in FIG. 1e , the etch-back process may, if the etchcontrast between the material of the side wall spacers 114 a, 114 b andthe material of the planarization layer 122 not is very strong, resultin a slight etch back of also the side wall spacers 114 a, 114 b.

With reference to FIG. 1f , subsequent to reducing the thickness of theplanarization layer 122 and the organic spin-on layer 116, a furtherspin-on deposition of an organic spin-on material is performed to coverthe structure 100. The further deposited organic spin-on material may beof a same material as the organic spin-on layer 116.

In the thickness reduction process illustrated in FIG. 1e , portions ofthe (first) organic spin-on layer 116 were left remaining in the gaps113. Accordingly, the further deposited organic spin-on material maycover also the remaining portions of the organic spin-on layer 116.Alternatively, the organic spin-on layer 116 may subsequent to thethickness reduction process illustrated in FIG. 1e be completely removedin the gaps 113. Accordingly, the further deposited organic spin-onmaterial may fill the gaps 113 between the mask features. In eithercase, the organic spin-on layer present in the structure 100 in FIG. 1f, whether deposited in a single or in two different depositionprocesses, will be referred to as the organic spin-on layer 124.

A patterned resist-based mask layer 128 is formed on the organic spin-onlayer 116. The mask layer 128 is patterned to include at least onetrench, extending in a direction transverse to the longitudinaldirection of the mask features.

An intermediate layer 126, corresponding to the intermediate layer 118,may be arranged between the organic spin-on layer 124 and the mask layer128 for improving the fidelity of a transfer of the pattern of thepatterned resist-based mask layer 126 into the organic spin-on layer124.

In FIG. 1g the pattern defined by the patterned resist-based mask layer128 has been transferred into the organic spin-on layer 124. The masklayer 128 may thereafter be stripped, optionally along with theintermediate layer 126, if present. At least one second trench 124′ hasaccordingly been formed in the organic spin-on layer 124. The secondtrench 124′ extends across and exposes the mandrels 112 of the maskfeatures.

Further etching is thereafter performed, of the exposed upper surfacesof the mandrels 112 in the second trench 124′, selective to the organicspin-on layer 124 and the side wall spacers 114 a, 114 b, until the masklayer 108 is exposed. The resulting structure is shown in FIG. 1 h.

In FIGS. 1g and 1h , a portion of the layer 124 has been cut-out toallow viewing inside the trench 124′.

A first etching chemistry may be used during the forming of the secondtrench 124′ in the organic spin-on layer 124. The first etchingchemistry may be the same as for the etching of the first trenches 116′.A second etching chemistry may be used during the etching of themandrels 112 to allow selective removal of the mandrel material,preserving organic spin-on material in the gaps between the maskfeatures. The second etching chemistry may include a HBr based plasma.It is also possible to use a Chlorine-based second etching chemistry.

The selective etching of each mandrels 112 inside the trench 124′results in, at the position of each mandrel 112 exposed in the trench124′, a hole 125 extending to the mask layer 108. Each hole 125 extendsbetween the pair of side wall spacers 114 a, 114 b of the respectivemandrel 112. Each mandrel 112 is thus divided into two separate parts,on opposite sides of a respective hole 125.

Similar to the discussion of the trenches 116′, the illustrated numberof trenches 124′ and their extension across at least three mandrelsmerely represent an example.

In FIG. 1i the structure 100 has been covered with a planarization layer132. The planarization layer 132 planarizes the structure 100. Theplanarization layer 132 covers the organic spin-on layer 124 and fillsthe trench 124′. The planarization layer 132 further fills the holesalong the mandrels 112. The planarization layer 132 may be of a samematerial and be deposited in a same manner as the planarization layer122. The planarization layer 122 may be referred to as a firstplanarization layer 122 and the planarization layer 132 may be referredto as a second planarization layer 132.

In FIG. 1j the thickness of the planarization layer 132 has been reducedto expose an upper surface of the mask features. The thickness reductionmay be achieved by an etch back process as described in connection withFIG. 1e . As shown, remaining material of the planarization layer 132form discrete second block masks 132′ along each mandrel which wereexposed during the forming of the trench 124′. Between each pair of sidewall spacers 114 a, 114 b a first mandrel portion 112 a and a secondmandrel portion 112 b are arranged, on opposite sides of a respectivesecond block mask 132′.

FIG. 1k , the mandrels 112 or mandrel portions 112 a, 112 b have beenremoved, selectively to the second block masks 132′ and the side wallspacers 114 a, 114 b. Thus, longitudinal gaps 134 have been formedbetween the side wall spacers 114 a, 114 b, at each position previouslyoccupied by a mandrel 112.

In FIG. 1k , material of the organic spin-on layer 124 remaining betweenthe mask features has also been removed, selectively to the first blockmasks 122′. The mask layer 108 is hence exposed in the gaps 113 betweenthe mask features. The organic spin-on layer 124 may be removed using anetch process including an oxygen-based or H₂/N₂-based etching chemistry.

The gaps 113 between mask features may be commonly referenced as a firstset of gaps 113. The gaps 134 between each pair of side wall spacers 114a, 114 b may be commonly referenced as a second set of gaps 134.

Each gap 113 is interrupted, in its longitudinal direction, by at leastone first block mask 122′. Each gap 134 is interrupted, in itslongitudinal direction, by at least one second block mask 132′.

In FIG. 1l , the mask layer 108 has been etched in the gaps 113 betweenthe mask features, and in the gaps 134 between each pair of side wallspacers 114 a, 114 b. The mask layer 108 may be etched using anysuitable dry etch process. For instance, a chlorine-based etchchemistry, possibly supplemented with additional gases such as CH₄ orHBr. In a dual layer mask layer 108 including a second layer 110 of SiN,an initial etch step with fluorine-based etching chemistry may beapplied first to expose the first layer 109, which subsequently may beetched as stated above.

During the etching of the mask layer 108 the side wall spacers 114 a,114 b, the first block masks 122′ and the second block masks 132′ act asa combined etch mask. A first set of trenches 136 a and a second set oftrenches 136 b are accordingly formed in the mask layer 108. Due to thepresence of the first block masks 122′ and the second block masks 132′the trenches 136 a, 136 b are interrupted in their respectivelongitudinal directions by remaining portions of the mask layer 108, theportions being formed at positions defined by the positions of the firstand second block masks 122′, 132′. The positions of the first and secondblock masks 122′, 132′ hence define the tip-to-tip locations for theconductive paths that are to be formed in the dielectric layer 106.

In FIG. 1m , the pattern of the mask layer 108 has been transferred intothe dielectric layer 106. Trenches 138 a corresponding to the trenches136 a, and trenches 138 b corresponding to the trenches 136 a arethereby formed in the dielectric layer 106. The pattern transfer may beperformed by an anisotropic etch process. The etch process may be aplasma-based etching process. The etch process may be a reactive ionetching (RIE) process. For instance, F-based plasmas may be used forselectively etching a silicon oxide dielectric layer 106 with respect tothe mask layer 108, including e.g. a layer of titanium nitride, titaniumoxide, hafnium oxide or zirconium oxide.

In case the mask layer 108 includes sub-layers 109, 110 the sub-layer110 may, in case it is formed by silicon oxide, be consumed during theetching of the dielectric layer 106. Moreover, during the patterntransfer also the side wall spacers 114 a, 114 b may be consumed.

Following the pattern transfer, the mask layer 108 (and the buffer layer108) may be removed.

The trenches 138 a, 138 b in the dielectric layer 106 may subsequentlybe filled with a conductive material to form the conductive paths orlines of the metallization level. The conductive material may be asingle metal such as Cu, Al or W, or alloys thereof.

The trenches 138 a, 138 b may be filled with a conductive material usingan electro-plating process, or a deposition process such as CVD or ALD.

The conductive material may be formed to overfill the trenches 138 a,138 b and thus cover surfaces of the dielectric layer 106 outside of thetrenches 138 a, 138 b. Such excess material may subsequently be removedby planarization and/or etch back to form the final conductive paths.

The above method steps may be supplemented with conventional processtechniques for via formation, in order to interconnect conducting pathsof different metallization levels.

In the above, the disclosure has mainly been described with reference toa limited number of examples. However, as is readily appreciated by aperson skilled in the art, other examples than the ones disclosed aboveare equally possible within the scope of the disclosure, as defined bythe appended claims. For instance, although in the above a method hasbeen disclosed in connection with forming of a second metallizationlevel above an already formed first metallization level 104, the methodmay be applied also for forming a first metallization level, or thirdmetallization levels or beyond. Moreover, in the above the mandrels 112were removed prior to removing remaining material of the organic spin-onlayer 124. The order of these process steps may however be reversed.

While some embodiments have been illustrated and described in detail inthe appended drawings and the foregoing description, such illustrationand description are to be considered illustrative and not restrictive.Other variations to the disclosed embodiments can be understood andeffected in practicing the claims, from a study of the drawings, thedisclosure, and the appended claims. The mere fact that certain measuresor features are recited in mutually different dependent claims does notindicate that a combination of these measures or features cannot beused. Any reference signs in the claims should not be construed aslimiting the scope.

What is claimed is:
 1. A method for defining patterns for conductivepaths in a dielectric layer, the method comprising: forming a mask layeron the dielectric layer, forming on the mask layer a set oflongitudinally and parallel extending mask features, each mask featureincluding mandrels having a pair of side wall spacers, the mask featuresbeing spaced apart such that gaps are formed between the mask features,depositing an organic spin-on layer covering the set of mask featuresand filling the gaps, etching a first trench in the organic spin-onlayer, the first trench extending across at least a subset of the gapsand exposing the mask layer, depositing in a spin-on process aplanarization layer covering the organic spin-on layer and filling thefirst trench, reducing a thickness of the planarization layer and theorganic spin-on layer by etching until upper surfaces of the maskfeatures are exposed, thereby forming, of remaining material of theplanarization layer, a discrete first block mask in each gap of thesubset of gaps, removing remaining organic spin-on material between themask features, selectively to each first block mask, thereby exposingthe mask layer in the gaps between the mask features, and etching themask layer in the gaps, thereby forming a first set of trenches in themask layer, at least one of the trenches being interrupted in alongitudinal direction.
 2. The method according to claim 1, furthercomprising, subsequent to reducing the thickness of the planarizationlayer and the organic spin-on layer: depositing an organic spin-on layercovering the set of mask features and each first block mask, etching asecond trench in the organic spin-on layer, the second trench extendingacross and exposing at least a subset of mandrels, and further etchingeach mandrel of the at least a subset of mandrels in the second trench,selective to the organic spin-on layer, to expose the mask layer,depositing in a spin-on process a planarization layer covering theorganic spin-on layer and filling the second trench, reducing athickness of the planarization layer and the organic spin-on layer byetching until upper surfaces of the mask features are exposed, therebyforming, of remaining material of the planarization layer, a discretesecond block mask along each mandrel of the at least a subset ofmandrels, removing the subset of mandrels, selectively to each secondblock mask, thereby exposing the mask layer between each pair of sidewall spacers, and etching the mask layer between each pair of side wallspacers, wherein each second block mask act as an etch mask, therebyforming a second set of trenches in the mask layer, at least one of thetrenches being interrupted in a longitudinal direction.
 3. The methodaccording to claim 2, wherein the first and second set of trenches inthe mask layer are etched simultaneously.
 4. The method according toclaim 2, wherein removing remaining spin-on-carbon material between themask features is performed subsequent to forming the one or more secondblock mask.
 5. The method according to claim 1, further comprising:transferring the trenches in the mask layer into the dielectric layer byetching the dielectric layer.
 6. The method according to claim 5,further comprising filling the trenches in the dielectric layer with aconductive material.
 7. The method according to claim 1, wherein themandrels include amorphous silicon or silicon nitride.
 8. The methodaccording to claim 1, wherein the side wall spacers include siliconoxide or silicon nitride.
 9. The method according to claim 1, whereinthe planarization layer is formed by a silicon-including spin-onmaterial.
 10. The method according to claim 1, wherein the mask layerincludes titanium nitride, titanium oxide, hafnium oxide or zirconiumoxide.
 11. The method according to claim 1, wherein the mask layerincludes a stack of a first material layer and a second material layer.12. The method according to claim 11, wherein the first material layerincludes titanium nitride, titanium oxide, hafnium oxide or zirconiumoxide and the second material layer includes silicon nitride or siliconoxide.